US President Donald Trump’s threats to annex Greenland and slap tariffs on its backers pose a challenge to Europe’s security, principles and prosperity, a top EU official said on Wednesday. “All these three dimensions are being tested in the current moment of transatlantic relations,” European Council President Antonio Costa said. He has convened an emergency summit of the EU’s 27 national leaders in Brussels today.

Trump’s determination to “acquire” the mineral-rich island in the Arctic region, for what he claims are security reasons, has undermined trust in the US among allies in Europe and Canada. Denmark angered Trump after sending a military “reconnaissance” force to Greenland, a semiautonomous Danish territory. A small number of troops from several European nations joined, and Denmark is weighing a longer-term military presence there.